Double balanced diode mixers are used to multiply or mix two electrical signals to produce a product signal. Such mixers have many applications in electronics and, particularly, in communications electronics. A known radio frequency (RF) mixer utilizes a diode quad connected between the secondary coils of two transformers. The diode quad usually consists of two diodes biased in the same direction connected between like terminals of the two transformers. The diode quad further consists of two additional diodes biased in the same direction but opposing the direction of the first two diodes and connected between unlike terminals on the two transformers. In this construction, the two additional diodes are criss-crossed between the terminals of the two transformers. An RF port and a LO (local oscillator) port of such mixers are formed by the terminals of the primary coils of the two transformers, and an IF (intermediate frequency) port is formed by two terminals connected to the mid-region of each secondary coil of the two transformers.
This type of conventional mixer has D.C. (direct current) response at the IF port, but the RF and LO ports have only A.C. (alternating current) response. For many applications, this frequency response is adequate. However, in some mixer applications, such as in a Costas Loop Type Phase Shift Keyed Demodulator, some of the mixers must have D.C. response on all three ports. To produce such D.C. responsive mixer, it is known to use multiplication techniques. However, this type of mixer is band width restricted to data rates below about 1 megahertz. For high data rates extending into the UHF range, a need exists for a mixer with three ports, each having a frequency response ranging from D.C. through the entire UHF band.